Sciencemadness Discussion Board

How to dry recrystallized KNO3?

Romix - 22-5-2021 at 17:15

Heating it in a beaker, it melts. And I think it sucks moisture from the air.

Romix - 22-5-2021 at 17:23

Want to drop copper from nitrate with Potassium Carbonate. And then recrystallize KNO3 and feed it to my plants.
What else could be in PCBs maybe nickel? Could there be anything that won't drop with addition of KCO3?
All solder removed first with weak acetic acid, before 3% nitric.
Tried recrystallizing pure KNO3 first, but having a problem drying it.

Johnny Cappone - 22-5-2021 at 17:38

Do you have large needle-shaped crystals, typical of the slow recrystallization of KNO3?
They are very beautiful, but unfortunately they retain water inside the crystal during crystallization. Once this happens, the only way to dry them is to grind them and take them to the oven or solar light in a container that allows a layer of up to 3 centimeters (if thinner, it will dry faster). Once this is done, you will no longer have problems with humidity. As far as I know (I'm too lazy to check the literature), no potassium nitrate hydrate is known. If you do not break the crystals to a finely divided powder, you will never be able to release the water that is trapped in them. One way to avoid this the next time is to promote a quick recrystallization, which tends to yield smaller crystals.

By the way, if you are heating KNO3 to its melting point, it is overheating and very quickly. A cup is also not the most suitable container for this type of procedure. The ideal is to use something that allows to spread the entire content in a thin layer, which should be as thin as the more hygroscopic the material you want to dry. The heating must be progressive and not more than enough to make the material anhydrous.

Romix - 22-5-2021 at 17:46

Thanks for your reply, yes I have large needle-shaped crystals.
Quote: Originally posted by Johnny Cappone  
Do you have large needle-shaped crystals, typical of the slow recrystallization of KNO3?
They are very beautiful, but unfortunately they retain water inside the crystal during crystallization. Once this happens, the only way to dry them is to grind them and take them to the oven or solar light in a container that allows a layer of up to 3 centimeters (if thinner, it will dry faster). Once this is done, you will no longer have problems with humidity. As far as I know (I'm too lazy to check the literature), no potassium nitrate hydrate is known. If you do not break the crystals to a finely divided powder, you will never be able to release the water that is trapped in them. One way to avoid this the next time is to promote a quick recrystallization, which tends to yield smaller crystals.

By the way, if you are heating KNO3 to its melting point, it is overheating and very quickly. A cup is also not the most suitable container for this type of procedure. The ideal is to use something that allows to spread the entire content in a thin layer, which should be as thin as the more hygroscopic the material you want to dry. The heating must be progressive and not more than enough to make the material anhydrous.

Romix - 22-5-2021 at 17:48

Pack they've been delivered to me in, have labels saying that it's flammable, is it safe to dry it in an oven ?

[Edited on 23-5-2021 by Romix]

[Edited on 23-5-2021 by Romix]

Johnny Cappone - 22-5-2021 at 18:00

Quote: Originally posted by Romix  
Pack they've been delivered to me in, have labels saying that it's flammable, is it safe to dry it in a on oven ?

[Edited on 23-5-2021 by Romix]


Is the symbol on the packaging the same as the one I sent as an attachment?
If so, it is not flammable, but an oxidizer (as expected for PURE potassium nitrate, without mixing). It means that it cannot catch fire by itself, but that it will (sometimes violently) burn combustible material (coal, cotton, powdered metals, sawdust, etc.). If what you have is pure KNO3, it is very safe to dry in the oven. Although make sure that the temperature does not rise above 100C, as this is unnecessary. In fact, even 50C will do the trick, it will just take a little longer.

1200px-GHS-pictogram-rondflam.svg.png - 51kB

Romix - 22-5-2021 at 18:19

Yes, same symbol, thanks.

Deathunter88 - 22-5-2021 at 21:58

KNO3 is not hydroscopic, you can dry it in the open.

Fyndium - 23-5-2021 at 02:33

I've been under impression that KNO3 is non-hygroscopic.

I spread my crystals onto a SS mesh on a drying rack and put a floor fan to push air from below. They dried very quickly.

maldi-tof - 8-6-2021 at 11:24

The information I know about KNO3 is that it is not hygroscopic, but it will cake badly.

I have dried KNO3 first in a fluidized bed/oven at 100 °C, but making sure it is well centrifugued, and then oven at 250 °C, and never had a problem, and finally get less than 0.5% loss on drying test.

Chemgineer - 9-6-2021 at 08:39

Potassium Nitrate is slightly hygroscopic, once dry I would keep it in an airtight container.

artemov - 10-6-2021 at 20:58

My KNO3 is dried in the oven for a couple of hours at 80C, then crushed.

https://www.sciencemadness.org/whisper/viewthread.php?tid=15...

Runic7 - 18-6-2021 at 21:43

It is not very hygroscopic, absorbing about 0.03% water in 80% relative humidity over 50 days. At 90-100% humidity it gets damp pretty darn quick, within a matter of hours making it useless for most pyrotechnic formulae. I recommend drying it in the oven at ~100 C to boil the water off. Be sure to store it in a sealed container with desiccant packets to keep it dry.

Romix - 22-10-2022 at 11:12

It sucked water from air because it was cut with something tasting like citric acid, now it's pure, recrystallized many many times.
It's tasteless now and my plants loving it.
Thinking about getting a 5kg of KNO3 from APCpure. Expensive though. I don't think so farmers pay that much when getting it in bulk. But what I don't want, them sending detectives to my house again...






[Edited on 22-10-2022 by Romix]